1. Field of the Invention
The present invention relates to a treatment apparatus and a treatment method for organic waste for safely and continuously decomposing organic waste containing polybiphenyl chloride (PCB), polyvinyl chloride, or radioactive substances etc.
2. Description of the Background
In recent years, in relation to the earth environmental problems, treatment of organic waste including harmful substances such as polybiphenyl chloride (PCB), decomposition retardant substances such as fron gas, resin such as polyvinyl chloride, or radioactive substances is a big problem. Generally, organic waste is treated by the incineration. However, by this incineration treatment method, many problems arise that poisonous substances such as dioxine and nitrogen oxide are generated and a large scale apparatus is required to collect those poisonous substances.
In recent years, as a method for decomposing organic substances, a method of using water (supercritical water) at a high temperature and a high pressure exceeding the critical point of water (temperature: 374° C., pressure: 22.1 MPa) has been noticed. The supercritical state means a state of a substance at a temperature and pressure exceeding the critical temperature and the critical pressure which are physical amounts intrinsic to an individual compound. A substance in this state is referred to as a supercritical fluid.
For example, a method of mixing an organic substance, water, and a fluid containing oxygen and oxidatively destructing the organic substance in the supercritical state exceeding the critical point of water is known, as discussed in Japanese Patent Publication No. Hei 1-38532 which is hereby incorporated by reference The supercritical water has an internal property between a liquid and a gas and is optionally mixed with an organic substance and oxygen, and thereby it is possible to oxidatively decompose an organic substance efficiently in a short time.
As the structure of a reaction vessel for realizing these reactions, there is a vessel type reaction vessel available, as discussed in Japanese Patent No. 2726293 which is hereby incorporated by reference. The vessel type reaction vessel has a structure that the upper part of the reaction vessel is used under the supercritical condition, and the lower part thereof is used under the liquid condition. Organic waste and oxygen are introduced from the upper part of the reaction vessel, and carbon dioxide obtained by decomposition of an organic substance is ejected from the upper part of the reaction vessel, and an inorganic substance is ejected from the lower part. This reaction vessel has an advantage that an inorganic substance having low solubility in supercritical water can be collected into a liquid on the lower part.
As for the upper part of the vessel type reaction vessel, to maintain the supercritical water condition, it is required to preheat waste and an oxidizer. Therefore, an introduction hole for introducing waste and an oxidizer at high temperature and high pressure into a reaction vessel at high temperature and high pressure is necessary. The introduction hole has a structure of being welded to or screwed into the reaction vessel. So that when a phenomenon that the temperature of waste is suddenly lowered is generated, a temperature difference is caused between the reaction vessel and the waste introduction hole. As a result, a difference in extension is caused between them, and a gap is generated between them, causing a leak. Therefore, the reaction vessel desirably has a structure and a constitution causing no temperature difference as much as possible.
Further, as an apparatus for treating corrosive substances, various reaction vessels having an anti-corrosive inner vessel installed in a pressure vessel have been proposed. For example, in Japanese Patent Disclosure No. Hei 9-85075, which is hereby incorporated by reference, inside the vessel type reaction vessel mentioned above, an anti-corrosive vessel is arranged and the inside and outside of the anti-corrosive vessel are controlled to the practically same pressure using high-pressure air. When high-pressure air is used, if a pin hole is formed in the pressure vessel during operation, air fed to maintain the same pressure is ejected outside the system. When air is opened from high pressure to low pressure, a very large volume expansion is caused, thus there is a great latent danger compared with a case where a liquid is used.
From the aforementioned, development of a safer treatment apparatus is desired for decomposing and reacting perfectly organic waste to a substance as a target